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It may have been Warped from getting to hot and some one re-torqued the head in an attempt to get the head gasket to seal?If it was warped and got brittle it would crack very easily.

Running lean,improperly set points,mouse hotel in the blower housing,worn cam lobe and blown head gasket will all cause an engine to overheat.I'm sure there are many more things that could make them run super hot.

It looks like 020 stamped on the piston in one of the pictures. I would guess that it has been rebuilt once already with a 20 thousands overbore.

I'm not an expert but I'd check the bore for out of round and put a feeler gauge next to the piston and cylinder wall to see what the wear is. You should be able to find the allowable clearance in a rebuild manual.

Also I'd lay a straight edge on the top of the block to see if it is level.. More than likely if it was mine I'd find a good head and a new gasket and put it back together.